Conventional methods for sealing electronic packages having a cavity therein (or “air cavity packages”) use adhesives to attach a package header (typically, a two piece package made from ceramic ring attached to a base with leads attached, or other similar materials and designs) and/or a package base/body combination (typically, a three piece air cavity plastic package that uses a base, a body or sidewall, and a lid) and a package lid mated together in known fixtures, sealing systems, “clip and bake” systems, or systems and processes for mating and sealing the components. In this regard, an organic adhesive is typically applied to a mating surface of a base, body and/or lid, and the parts are aligned and put into contact. Pressure is applied to the interfaces between the pieces, and the adhesive are heated until the adhesive is cured, sealing the package.
In early prior art, most electronic package sealing was accomplished by starting with the assembly of two or more pieces (e.g., a base and a lid) with an adhesive, all starting at or near room temperature. Heat and mechanical force (e.g., clamping) would then be applied to keep the assembly in alignment and to cause the adhesive to flow and cure.
However, using such procedures often resulted in undesirable anomalies such as “pin holes” or “blowouts.” Specifically, when the adhesive between clamped pieces is heated from room temperature to its curing temperature, the adhesive becomes soft and sticky and the clamping force causes it to flow and make a leak-free seal. However, this seal entraps and contains whatever volume of gas (e.g., air, inert gas, etc.) that is within the package pieces at that time. The result of continued heating causes the gas pressure in the package to rise, and because the higher temperature also causes the adhesive to become thinner (i.e., have a lower viscosity), its ability to hold the gas is diminished, forcing gas through the seal and creating blowouts or pin holes.
With some adhesives (e.g., such as B stage adhesives), as it is subjected to heat, it transitions from a solid to a liquid. As the adhesive continues to heat, it advances to a hardened state. At early stages of heating, if the adhesive has not advanced to a semi-hardened state, when a blowout occurs the adhesive can reflow and fill the hole. However, if the adhesive has hardened too much, it may not be able to reflow over the blowout, leaving a pin hole or blowout.
Attempts to reduce blowouts such as those disclosed in U.S. Pat. No. 5,056,296 entitled “Iso-Thermal Seal Process for Electronic Devices” have included preheating package components along with the mating surfaces that have been coated with an adhesive prior to mating the components and applying pressure. For example, with reference to FIG. 1, by preheating the base 101 and the lid 102 while keeping the base 101 and the lid 102 separated, a temperature equilibrium (Te) is created amongst the components and, importantly, the air space therein. Because equilibrium is obtained prior to mating, the pressure differentials are reduced, thus reducing or eliminating blowouts in the thermosetting adhesive 103. While a positive pressure may remain after the lid makes contact with the body by virtue of the closing of the cavity, the remaining pressure generally will not be sufficient to cause pin holes or blowouts.
However, while such preheating is an effective solution for preventing blowouts, it has some disadvantages as well. For example, preheating requires a waiting period for the temperature of the components to rise to the desired level. During this waiting period, no other processing can take place on the package. Depending on the mass of the package components, this waiting period can last several minutes, limiting the number of sealed packages that can be produced over a given time period (e.g., units per hour or “UPH”).
Additionally, using existing manufacturing processes, obtaining a sealed package that has consistent alignment and height each time can be challenging. Among other reasons, contributors to inconsistent alignment and height include variations in the specifications of the components that make up the package (e.g., base, lid, epoxy thickness variations, etc.). These components have their own specifications and tolerances. When the tolerance extremes (e.g., high end for lid, high end for base, etc.) are compounded, inconsistencies in alignment and height are exacerbated. Likewise, bond line thicknesses may vary depending on factors such as the amount of adhesive applied, the pressure applied during the sealing process, the heat up and flow out of the adhesive, and the like.
As new technologies develop which reduce the cost for air cavity electronic packages, the demand for the packages increases. Thus, to meet this demand, apparatus, systems, and methods that increase UPH yet maintain the quality and integrity of the packages produced, are desirable.